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Citrograph

Testing for HLB at CRB Riverside Lab

PREMIER ISSUE

January/February 2010 Citrograph 3

IN THIS ISSUE

4 President’s Message

5 Industry Views

6 Events Calendar

7 Asian citrus psyllid and quarantines

8 How serious is the threat of Asian citrus psyllid and Huanglongbing?

12 Citrus Research Board aggressively responds to unprecedented threat

14 ‘DaisySL’ Mandarin

16 Vision Robotics successfully tests scout robot

20 Topworking or replanting, A grower’s perspective?

22 Citrus quick decline: a disease complex

Citrograph is published bimonthly by the Citrus Research Board, 323 W. Oak Street, Visalia, CA 93291. Citrograph is sent to all California citrus producers courtesy of the Citrus Research Board. If you are currently receiving multiple copies, or would like to make a change in your Citrograph subscription, please contact the publication office (above, left).

Every effort is made to ensure accuracy in articles published by Citrograph; however, the publishers assume no responsibility for losses sustained, allegedly resulting from following recommendations in this magazine. Consult your local authorities.

The Citrus Research Board has not tested any of the products advertised in this publication, nor has it verified any of the statements made in any of the advertisements. The Board does not warrant, expressly or implicitly, the fitness of any product advertised or the suitability of any advice or statements contained herein.

An Official Publication of the Citrus Research BoardJAnuARy/febRuARy 2010 • Volume 1 • numbeR 1

PUBLICATION OFFICE

U.S.Single Copies: $1.501-Year Subscription: $15.002-Year Subscription: $28.00

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Cover photo: Testing for HLB at CRB Lab in Riverside – photo by Tyler Joe, Riverside

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Margie Davidian, EditorDr. Beth Grafton-Cardwell, Senior Science Editor

Dr. Akif EskalenBen Faber, Ph.D

Ted BatkinRichard Bennett

EDITORIAL BOARD

4 Citrograph January/February 2010

EDITORIAL BY TED A. BATKIN

President’s Message

Welcome to the premier edition of Citrograph!! The members of the Citrus Research Board are proud to present the re-birth of an old friend to the industry for the past 90 years or more. Citrograph has been the primary communications vehicle for producers of fresh citrus crops since its origin

in the 1920’s. During our meetings with growers for the past 10 years, one consistent message was to “bring back Citrograph magazine” as part of our grower education program. This year we were fortunate to partner with a very well known publishing company, Farm Progress Companies, to once again bring you this very informative and useful magazine.

The Board has formed an Editorial Board of growers, writers and UC Cooperative Extension specialists to present content and format that we hope will meet your needs. A few of the planned features are articles from University scientists, both California and other states; feature articles from the various industry organizations; articles from growers regarding new and novel techniques that they are willing to share; historical pieces featuring comments from the past and present plus future outlooks; articles on organics and small farm production; home recipes for the increased use of citrus; and many, many more subjects.

As a young grower I remember waiting for each issue of Citrograph to arrive. I would take it in my pickup and read it while waiting for the water runs to complete before changing the furrows…yes, I am really that old… We hope that this new publication will bring all of you that same anticipation while managing your water runs from your computers or monitoring the weather reports in anticipation of another frost night.

District 2 – Southern California – Coastal

Member AlternateEarlRutz,Pauma Valley AlanWashburn,RiversideWilliamPidduck,Santa Paula JamesFinch,Santa PaulaJoeBarcinas,Riverside KenKelley,Hemet

District 1 – Northern California

Member AlternateAllanLombardi,Exeter KevinSeverns,Orange CoveDonaldRoark,Lindsay DanDreyer,ExeterJimGorden,Exeter DanGalbraith,Porterville JoeStewart,Bakersfield FrancoBernardi,VisaliaEtienneRabe,Bakersfield RichardBennett,VisaliaJohnRichardson,Porterville JeffSteen,StrathmoreKevinOlsen,Pinedale DavidDir,Visalia

CITRUS RESEARCH BOARD MEMBER LIST BY DISTRICT 2009-2010

Citrus Research Board323 W Oak, Visalia, CA 93291PO Box 230, Visalia, CA 93279

(559) 738-0246FAX (559) 738-0607

E-Mail [email protected]

District 3 – California Desert

Member AlternateWilliamStein,Oasis JohnTurco,Indio Public MemberMember Alternate SeymourVanGundy,Riverside SteveGarnsey,Fallbrook

The Mission of the Citrus Research Board:

Develop knowledge and build systems for grower vitality. Focus on quality assurance, clonal protection, production research,

variety development, and grower/public education.


INDUSTRY VIEWS

“How do you see mandarins affecting the overall citrus industry?”

How the mandarin will affect the citrus industry is an interesting question. Many of those in the industry fear a cannibalization of the navel consumption and perhaps to some

degree that may be true. Having said that, I feel the mandarin has created new demand for the citrus category. There is an excitement in the marketplace for the mandarin or Clem-entine that may pull consumers into citrus that were previously not too interested, young children, as an example. It is easy to peel, a convenient size, and nature has provided very green packaging! This enthusiasm may spill over to other varieties, assuming those varieties will also deliver great taste and pleasurable experience. This, in a circuitous way, may help the citrus industry evolve into a more consumer-oriented business. If we consistently provide a great product, people will re-purchase throughout the season, thus pulling our product through the system. I cannot emphasize this enough- sweet juicy, colorful oranges will sell over and over. Oranges need to be harvested at the peak of freshness, not when the market is high or a grower demands pick equity. Also, poor varieties produce a poor end product. We only need to look at our neighbors in the stone fruit industry and learn a valuable lesson!

I would hope the enthusiasm in the marketplace for the easy peel mandarin varieties will spill over to other categories and be a positive influence on the citrus industry as a whole! — Loren Booth, Owner/President, Booth Ranches, flanked by her children, Jake Sill and Blair Moffett

Very positively! A truly new product superior or equal to the best of those citrus selec-tions to date and we are capitalizing on the find in many different partitions of the

California citrus industry. The positive starts from the robust nursery industry, now growing more trees than in the past, and growers have an option other than navels, lemons and grapefruit for replacement citrus. The packing industry gets to innovate the equipment, and the progressive managers continue on the path of improved citriculture. The profits of the industry are not only through capitalism but the consumers now have a wonderful alternative or choice in the grocery market with great tasting and easy to manage fruit. Positive change is what folks want, and now we have the opportunity to embellish it. We rarely have serendipity of such magnitude – that is finding these new easy peel citrus fruits, or perhaps it’s all in nature’s timing. — Tom Mulholland, CEO, Mulholland Citrus

asks:Citrograph

Mandarins are a positive complement to the overall citrus category. Taste will al-ways drive fruit consumption. We are experiencing resurgence in citrus demand

due to the expansion in citrus varieties. As we emerge from one of the most difficult economies in generations, we have been fortunate to experience increased demand in various varieties of specialty citrus: Clementines, W. Murcotts, Cara Caras, Minneolas, Moros, Gold Nuggets, Pixies, and others.

Canada and Europe may be indicators of what the future holds for the US market where tangerines, tangelos and mandarins represent 36-41% of the orange/easy peeler category. They’ve had access to specialty citrus from around the world for years. The future will be bright for citrus as we continue to develop new and better tasting varieties. This is particularly important as the competition for shelf space and restaurant menus increases with fruit from around the world. — Kevin Fiori, VP, Sales & Marketing, Sunkist Growers Inc.


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feb 9-11 World Ag expo International Agri-Center Tulare, CA

feb 18 CRb-uCCe Citrus Research Grower Seminar Pala Casino Hotel Pala, CA

feb 19 CRb-uCCe Citrus Research Grower Seminar Indian Palms Country Club Indio, CA

feb 24-26 CRb new Technologies Conference berkeley, CA

mar 4 California Citrus mutual Citrus Showcase Visalia Convention Center Visalia, CA

mar 22-23 uC extension Citrus Postharvest Conference Santa barbara, CA

mar 24 CRb-uCCe Citrus Postharvest Seminar exeter memorial building exeter, CA

mar 25-26 CRb Research Review CRb board meeting Doubletree Hotel ontario, CA

Jun* Citrus Institute noS events Center San bernardino, CA

Jul 8 CRb board meeting Ventura, CA

Jul* CRb-uCCe Citrus Research Grower Seminar Santa Paula, CA

Aug* CRb-uCCe Citrus Research Grower Seminar exeter, CA

Sep 22-23 CRb Research Proposals CRb board meeting Doubletree Hotel bakersfield, CA

oct* CRb-uCCe Citrus Research Grower Seminar northern California

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2010 EVENTS CALENDAR

Sandy Creighton, Sales Manager Phone: 559-433-9343

E-mail: [email protected]

Contact us today to be included in future issues

of Citrograph

Reach Commercial California &

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tion equipment, fertilizer or pesticides...consider the value of your ad dollar in the pages of Citrograph.

Each issue reaches every commercial citrus grower in the states of Califor-nia and Arizona, plus associated business members affiliated with the citrus industry...the people in charge of purchasing. Your advertising message is directed to farm leaders who use vast amounts of goods and services.

Circulation reaches over 5,000 key decision makers among California and Arizona fresh citrus growers, landowners and industry-involved com-panies. In the near future, Citrograph will reach the entire United States.

Don’t miss the next issue!


The first question should be “What is a quarantine and where do the requirements originate?” Quar-

antines are regulations designed to pre-vent the spread of a known or suspected pest to areas where they are unknown. Based on the best available science, United States Department of Agricul-ture (USDA), California Department of Food and Agriculture (CDFA) and our national and international trading partners develop rules and procedures governing surveying, treatments and prohibitions to allow the movement of produce and plants with reasonable as-surance that they are safe from spread-ing the pest. Our industry partners are important participants in the process.

Readers of this publication probably are familiar with Asian Citrus Psyllid (ACP), the known vector of arguably the world’s most dreaded citrus disease: Huanglongbing (HLB), which is also called “Citrus Greening Disease.” ACP and HLB originated in Asia or India but have spread to nearly every citrus grow-ing area in the world. Before arriving in the United States, it wreaked its destruc-tion in South America, especially Brazil.

ACP was discovered in Florida, but because of their quarantine regu-lations of citrus plants, they believed they did not have HLB. Since the insect alone causes little damage and can be controlled with insecticides commonly used for other citrus pests, no effort was made to control it, and it rapidly spread throughout the state. Unfortunately, everyone does not obey quarantine laws and the disease was found in a pummelo that had been brought into Florida from Asia and planted in a homeowner’s yard. This was probably only one of many instances where the disease had arrived and without the ACP to spread it, the originally infected tree was sick for a number of years but went undetected.

The second problem was that the ornamental plant Murraya paniculata,

Bob Atkins, San Diego County Agricultural Commissioner

Asian citrus psyllid and quarantines

orange jessamine, was not recognized as being susceptible to HLB and so was allowed to be shipped as cut flowers and nursery stock. The psyllid reproduces really well on this plant and so these shipments moved ACP rapidly around the state. This also proved to be a disaster in Florida, because this plant helped to spread the disease. HLB is a particularly nasty disease because it surely causes the death of the plant and because the disease may lie undetectable for up to 5 years. Murraya was also shipped to California before it was known to carry HLB or other citrus diseases. It was in 2006 that USDA/APHIS put restrictions on the movement of Murraya.

ing with pesticides all plants in the citrus family (Rutaceae) within 400 meters of where ACP was found. Then disaster struck LA and Orange Counties (OC) in August 2009. The OC find in Santa Ana has remained small and contained at less than a dozen infested properties. The LA finds are over 550 infested properties and include thousands of properties needing treatment within 400 meters of those sites. The infestations are concentrated near downtown LA, but are also scattered southeast to La Mirada and to the east along Interstate 10 through El Monte to Walnut and Pomona. Currently, all of Imperial, Orange and LA, most of San Diego and much of Riverside and San Bernardino Counties are quarantined. Tucson County, Arizona has just been included. The ACP infestation continues to be treated on both sides of the U.S./Mexico border. The ACP specimens re-covered are tested for HLB and all have been negative for the disease to date.

The quarantine is designed to limit spread of ACP. First, citrus fruit must be free of leaves and stems and be washed or brushed to remove ACP before leav-ing the quarantine area. In addition, many of the citrus packinghouses are demanding that all fruit arrive free of leaves. Secondly, no citrus plants may leave the quarantine area. Wholesale citrus nurseries are required to treat plants before shipment to retail stores in the quarantine area in order to protect them from becoming infested with ACP. Finally, all citrus green waste must be chipped and mulched and dried or dou-ble-bagged before it can leave the area.

Money for eradication is a challenge. CDFA has exhausted their eradication funds for the fiscal 09/10 year, and USDA is hampered by Environmental Impact Report requirements to fund the treat-ments. It has been agreed that strong efforts are needed to survey the citrus growing areas of California for ACP. Also, the LA infestation needs intensive testing of the ACP and infested trees for HLB, to find and eradicate the disease before the vector can spread it.

Once we know where the ACP is and is not throughout California, we can formulate strategies for eradication and control of the potentially devastating ACP/HLB. Meanwhile, we must assure these pests are not moved by growers, nurseries or the public by enforcing these quarantine requirements. l

Wemustassurethesepestsarenotmovedby

growers,nurseriesorthepublicbyenforcingthesequarantinerequirements.

In June 2008 USDA trapping along the California/Baja California, Mexico border, found ACP. In response, San Diego County and CDFA placed yel-low sticky panel traps throughout the residential areas of the county. Those traps found the infestation had gotten across the border, and a CDFA/USDA quarantine was proposed. USDA had up to that point quarantined entire coun-ties, not portions. San Diego and CDFA argued successfully that the counties in the eastern states were much smaller in area than those in California. It was decided that a 20-mile radius around an ACP find would be quarantined, which spared the majority of the commercial citrus production and all 4 of the citrus producing nurseries in the County.

For over a year, the ACP infestation was controlled and slowed in San Diego and Imperial Counties by CDFA treat-


By now you have heard the news that a tiny insect, about the size of an aphid, has arrived in south-

ern California and has the potential to cause great harm to the citrus industry. The Asian citrus psyllid can attack all cultivars of citrus and closely related plants in the Rutaceae family such as Indian curry leaves (Bergera koenigii), orange jasmine (Murraya paniculata) and Chinese box orange (Severinia buxi-folia). When it feeds, the psyllid injects a toxin that causes young leaf flush to twist and curl or fall off completely.

The psyllid is a damaging pest by itself, but we can control the damage it

How serious is the threat of Asian citrus psyllid and Huanglongbing?

causes to leaves through biological and chemical controls. There are a number of coccinellid predatory beetles that readily feed on the nymphal stages and a small parasitic wasp called Tamarixia that deposits its egg under the nymph and parasitizes it. ACP is also fairly sus-ceptible to a wide range of insecticides. The more serious problem with this pest, is that this insect is a very effective car-rier of a bacterial disease called Huan-glongbing (HLB), also known as citrus greening. HLB is devastating to citrus trees. The trees grow poorly and produce small blotchy yellow leaves. Fruit grow slowly and asymmetrically, and tend to

fall of the tree prematurely. The juice turns off-flavor and the

tree may die within 3-5 years after it is infected. There is currently no cure for the disease, so HLB is a death sentence for citrus trees. In Florida, where both the psyllid and the disease are found, citrus growers are destroy-ing tens of thousands of HLB-infected trees each year to prevent the disease from spreading.

The psyllid arrived in Florida in 1998 and within

3 years it spread through-out the state of Florida,

through natural flight and also by hitchhiking on orna-

mental orange jasmine plants from nurseries to retail stores

to homeowner yards. Florida did not realize the level of damage that

this pest could cause and did not try to stop it. Florida is now realizing that the ornamental orange jasmine can also be a carrier of the HLB disease pathogen and this plant has helped to spread both the insect and disease around the state. Currently, citrus trees in 32 counties in Florida are known to have HLB and both the psyllid and disease have spread from the urban areas into commercial citrus.

The psyllid was observed in 2006 in the state of Sonora, Mexico by Dave Headrick of Cal Poly San Luis Obispo and Jim Stewart and Bert Quezada of Exeter, while they were visiting citrus orchards in that area in search of citrus peelminer parasites. In 2008 it was found in San Diego and Imperial counties and in 2009 in Orange and Los Angeles counties of California. Up to this point, the majority of California finds have been in citrus trees and Murraya bushes in yards of homeowners. In an effort to slow the spread of the psyllid and learn from the Florida experience, the Califor-nia Department of Food and Agriculture (CDFA) and the Citrus Research Board (CRB) established a Huanglongbing Task Force to study the science of the situation, establish regulations to limit spread of the psyllid and disease, and to communicate information to the citrus industry and general public. CDFA set up quarantines 20 miles around the ini-

By Dr. Beth Grafton-Cardwell


tial psyllid finds, required treatment of Rutaceae in retail stores and restricted movement of Rutaceae out of the quar-antine area to limit ACP hitchhiking on plant material. Harvested fruit within the quarantine areas must be cleaned and free of plant material (leaves and stems) that the psyllid could ride on before being shipped out of the quaran-tine areas. Finally, citrus and Murraya in yards infested ACP and adjacent yards are treated by CDFA with a combina-tion of systemic imidacloprid and the foliar pyrethroid cyfluthrin in an attempt to eradicate the psyllid. The majority of treatments have suppressed psyllids for up to a year. However, the psyllid continues to spread because it is difficult to detect. It is a very small insect that is attracted to the yellow sticky cards only at certain times of the year.

At the moment, although portions of southern California are infested with the psyllid, the HLB disease has not been found in California. That may lead you to ask why we should worry about the disease, and there is a simple answer: because HLB-infected trees have been found in Mexico and the disease is likely to work its way to California. HLB-associated bacteria may be carried in the bodies of psyllids or be brought to California inside an infected citrus plant. In Florida, there is good evidence that the disease arrived from Asia in plant material used for backyard plantings of citrus and the disease remained in those yards, not spreading, until ACP arrived to pick it up and move it around. California could be in a similar situation, with an infected backyard tree acting as a catalyst for spread of the disease.

The best way to keep the disease from finding its way here is to keep the psyllid populations very small, prevent Rutaceae from entering California from other states or countries, and to plant only locally grown certified disease-free citrus trees. Because of the high percent-age of yards with citrus in California, the general public is a critical component of the plan for controlling ACP and HLB. The CDFA, the USDA and the CRB have launched massive public awareness programs through mailings, internet web sites, television, newspapers and radio to educate the urban population. You can help with this effort by teaching friends and relatives to check their citrus regu-larly for signs of the psyllid and symp-

toms of this disease. This can be done by utilizing the Citrus Research Board web site www.californiacitrusthreat.org. The web site provides information about who they can call if they think they have found the insect or disease. If a homeowner lives in a psyllid-infested region, they need to be careful to dry out or double-bag landscape clippings to prevent moving the live psyllids to new areas. Bayer Corporation has a new cit-rus formulation of imidacloprid (Bayer

Advanced fruit, citrus and vegetable) that homeowners will be able to apply themselves to reduce ACP infestations. Most importantly teach friends and relatives the dangers of moving plants into and around California and sharing untested grafting material.

Asian citrus psyllid and the potential threat of HLB is rapidly altering the way the California citrus industry does business. Citrus nurseries are required to apply pesticide treatments prior to

shipping plants to retail stores within quarantine zones. Citrus nurseries are building very expensive screenhouses with fine mesh to protect their trees from infestation by ACP and maintain disease-free plants. Citrus growers in quarantine areas must clean fruit before shipping it to be packed in other regions. ACP is likely to be found in commercial citrus orchards in southern California in the very near future. The citrus industry with the help of the University of Cali-

fornia is developing plans for areawide insecticide treatments of commercial citrus. These treatments include systemic imidacloprid and foliar applications of organophosphates (Lorsban, Dimetho-ate, Imidan), pyrethroids (Baythroid and Danitol) and Delegate. Unhappily, none of the registered organic insecticides tested (Pyganic, Neemix, oils, Surround, Ecotrol) show enough efficacy to pro-vide an adequate control program for organically grown citrus. The proposed

Yellow sticky trap for collecting adult psyllids.

AsiancitruspsyllidandthepotentialthreatofHLBisrapidlyalteringthewaythe

Californiacitrusindustrydoesbusiness.


treatment strategy is to treat the psyllid aggressively in the fall and late winter with the broad spectrum foliar insecti-cides when the population is primarily adults and utilize systemic insecticides and additional foliar insecticides when the nymphal populations appear during periods of flush. An areawide approach is critical because the insect is small and difficult to detect visually and yellow trap cards are not effective when flush is present. Thus, it is difficult to determine the boundaries of a psyllid infestation and they are known to fly many miles. The Florida experience demonstrated that delayed action resulted in rapid spread of the psyllid and the disease.

The disease has existed for many years in Asia and India yet citrus con-tinues to be grown there and China has become one of the leading citrus produc-ers. How can their industries survive in the face of the disease? The answer is that their expectation of fruit quality and tree productivity is much lower than Califor-nia. The lifespan of trees in HLB infected regions is less than 15 years and the productivity of the trees is much lower than in California. In some areas of China, citrus production con-tinuously moves to new areas in order to stay ahead of the psyllid and disease. Florida is los-ing citrus rapidly because urban areas and untreated orchards provide continuous sources of psyllids and patho-gen. There is much question about how severe the disease will be in California. California has a dryer climate

HLB infected leaves showing asymmetrical blotchy mottle yellowing.

HLB infected fruit showing asymmetrical segments and aborted seeds.

than Florida, with less frequent flushing of trees, and fewer alternate ornamen-tal host plants such as orange jasmine. In the San Joaquin Valley, extremes of heat and cold could act to reduce psyllid survival and suppress the bacteria. While this may make the situation less dire for California, it is not likely to stop the pest and disease altogether. Thus, the citrus industry must take a conservative ap-proach to slow the spread of the psyllid to protect against the disease.

Federal, State, and citrus industry funds are being directed not only towards ACP eradication efforts in California, but also towards research programs throughout the nation. Re-searchers are screening the effectiveness and residuality of insecticides to provide

new and different insecticide classes to manage the problem of ACP resistance to insecticides. Research is underway to develop better trapping systems that utilize the insect’s attraction to pheromones and color cues. A critical problem with HLB management is that symptoms often don’t show in a tree for 6 mo to 2 years or longer after becoming infected and these trees can be a source of infection for neighboring trees during that time period. Scientists are working to improve HLB detection methods so that the disease can be detected before symptoms appear and infected trees can be removed more promptly. The most critical research effort in progress is the development of a citrus tree that can withstand the disease. The current ACP insecticide treatment strategy is an effort to limit the numbers and spread of ACP in order to buy time for this re-

search to be accomplished. Once HLB is found, the ACP control strategy

will shift to directly protecting trees from infection.

Huanglongbing is the most serious disease of citrus worldwide. The citrus in-dustry must do everything it can to educate itself and the general public, reduce ACP populations, care-fully control movement of plant material to limit the introduction of HLB,

and fund creative research to solve this very difficult

problem. l

Dr. Beth Grafton-Cardwell is Research Entomologist, Uni-

versity of California Riverside and Director of Lindcove Research and Extension Center.


PlasterCity

NilandCalipatria

Andrade

GlamisOgilby

MERCED

FRESNO

SANTA CLARA

INYO

SANTA CRUZ

SAN BENITO

MONTEREY TULARE

KINGS

SAN BERNARDINOKERNSAN LUIS OBISPO

SANTA BARBARAVENTURA

LOS ANGELES

Sa Santa Rosa Islan

ORANGE

IMPERIAL

SAN DIEGOn Nicolas Island

San Clemente Island

RIVERSIDE

MADERA

TecateTijuana San Luis Rio

Colorado

Baja California

Sonora

SantaMonica

LakewoodLongBeach

Anaheim

NewportBeach

SanJuan

Capistrano

SanClemente

RiversideSanJacinto

Big BearLakeSan

Bernardino

OceansideEscondido

Del Mar

Palos Verdes Estates

ImperialBeach

San Diego

Pasadena Azusa

San Diego CountryEstates

JulianRamona

AlpinePineValley

AZ

NV

United States Department of Agriculture

Animal and Plant Health Inspection Service

Date Created: December 14, 2009

Data Source:CA Dept of Food & Agric.USDA, APHIS, ISTeleAtlas Dynamap

USDA, APHIS, PPQWestern Region GIS Specialist650 Capitol Mall, Suite 6-400Sacramento, CA 95814

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service collected the data displayed for internal agency purposes only. These data may be used by others; however, they must be used for their original intended purpose.0 10 20 30 40 505

Miles

Asian Citrus Psyllid Cooperative ProjectCalifornia, Arizona, and Baja California

Coordinate System:CA Teale Albers, NAD83

LegendACP Traps_Citrus Research Board_12-10-09

Asian Citrus Psyllid, CA_8-27-08 thru 12-9-09

Asian Citrus Psyllid, AZ_10-20-09 thru 12-3-09

Asian Citrus Psyllid, Mexico_6-19-08 thru 12-5-09

California Quarantine for ACP 11-17-09

Arizona Quarantine for ACP_12-7-09

Parks in CA

National

State

Local

August 2008 brought an event that the California citrus in-dustry had hoped would never

come – Asian citrus psyllid (ACP) was found in California. Although the Citrus Research Board (CRB) had already been developing an action plan in the event ACP was detected in California, the news was still very unsettling. “We had been monitoring the movement of ACP for the last 10 years and knew it was a very likely possibility that ACP would ultimately find its way into California,” said Ted Batkin, CRB President, “but on that August day when the news came we all paused for a moment as we realized things would now significantly change.” Since that first ACP confirmation in southern San Diego County in 2008, things have changed.

The threat to California’s citrus is not directly from ACP but from Huanglong-bing (HLB), the disease Asian citrus psyllid carries. HLB, also known as citrus

Citrus Research Board aggressively responds to

unprecedented threat

Joining the CRB staff was Dr. Mary-Lou Polek, CRB Vice President of Science and Technology. Polek, an experienced plant pathologist, came to CRB following a fourteen-year tenure with California Department of Food and Agriculture (CDFA), most recently as program manager and plant patholo-gist for the Central California Tristeza Eradication Agency. “As we looked at the scope of the problem we realized that our best plan would be to establish as broad of a commercial trapping grid as possible,” stated Polek, “and at the same time build the crucial lab testing

Gorden, CRB Chair and Lemon Cove grower. “We decided to build a program that would trap for ACP in commercial groves and conduct tree sampling for HLB. Our intent is that when ACP finds occur, or in the event HLB is located, to quickly alert growers who can then take the appropriate action to reduce the spread of the psyllid or disease.”

The increase in CRB programs required additional resources. At the request of the industry, the California Department of Food & Agriculture (CDFA) conducted a referendum in the fall of 2008, and a strong majority of the growers approved an amendment to the Program raising the cap for the maxi-mum allowable assessment rate from 3 cents to 9 cents per 55-pound field box. “No one is ever thrilled with the idea of paying more, but we as an industry knew that our only hope in California against ACP/HLB would come if we collectively provided the resources necessary to con-duct an effective program,” said Gorden.

Call to Action!CRB Operations –Field, Lab, Data Management

With an overwhelming mandate from California’s citrus industry to battle the threat from ACP/HLB, the Citrus Re-search Board began to ramp up opera-tions with the following goal: to protect the California citrus industry from the devastating result of allowing ACP/HLB establishment. An unprecedented model was developed by the CRB to provide the California citrus industry the best ACP/HLB detection system in the world. The scope of operations includes: trapping and inspection for ACP, testing both plant samples and insects for HLB, and developing a map-based website that couples the field data with the lab results. Data resulting from this operation will be extended to the grower community and those advising them, allowing for the implementation of area-wide insect and disease management strategies.

greening disease, is a bacterial infection that attacks citrus trees and causes bitter, inedible fruit and inevitably kills the tree. HLB has wreaked havoc in Florida since it was first confirmed in 2005, and it is estimated that 10-12% of their industry is being destroyed annually. To date there have been no positive finds of HLB in California, but history tells us that where ACP goes HLB is sure to follow.

“We know that ACP is the vector for HLB and as a Board [CRB] we decided our best offense was to aggressively launch a two-pronged attack,” said Jim

Preparing to isolate and lift ACP caught on sticky panel trap.


PlasterCity

NilandCalipatria

Andrade

GlamisOgilby

MERCED

FRESNO

SANTA CLARA

INYO

SANTA CRUZ

SAN BENITO

MONTEREY TULARE

KINGS

SAN BERNARDINOKERNSAN LUIS OBISPO

SANTA BARBARAVENTURA

LOS ANGELES

Sa Santa Rosa Islan

ORANGE

IMPERIAL

SAN DIEGOn Nicolas Island

San Clemente Island

RIVERSIDE

MADERA

TecateTijuana San Luis Rio

Colorado

Baja California

Sonora

SantaMonica

LakewoodLongBeach

Anaheim

NewportBeach

SanJuan

Capistrano

SanClemente

RiversideSanJacinto

Big BearLakeSan

Bernardino

OceansideEscondido

Del Mar

Palos Verdes Estates

ImperialBeach

San Diego

Pasadena Azusa

San Diego CountryEstates

JulianRamona

AlpinePineValley

AZ

NV

United States Department of Agriculture

Animal and Plant Health Inspection Service

Date Created: December 14, 2009

Data Source:CA Dept of Food & Agric.USDA, APHIS, ISTeleAtlas Dynamap

USDA, APHIS, PPQWestern Region GIS Specialist650 Capitol Mall, Suite 6-400Sacramento, CA 95814

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service collected the data displayed for internal agency purposes only. These data may be used by others; however, they must be used for their original intended purpose.0 10 20 30 40 505

Miles

Asian Citrus Psyllid Cooperative ProjectCalifornia, Arizona, and Baja California

Coordinate System:CA Teale Albers, NAD83

LegendACP Traps_Citrus Research Board_12-10-09

Asian Citrus Psyllid, CA_8-27-08 thru 12-9-09

Asian Citrus Psyllid, AZ_10-20-09 thru 12-3-09

Asian Citrus Psyllid, Mexico_6-19-08 thru 12-5-09

California Quarantine for ACP 11-17-09

Arizona Quarantine for ACP_12-7-09

Parks in CA

National

State

Local

facilities that would process the samples as we worked to detect ACP and HLB.”

Brian Taylor was added to the team as Field Director, a natural selection considering his thirty years experience with CDFA in directing detection and eradication activities on a wide variety of exotic pests. According to Taylor, CRB field technicians are currently servicing traps in San Diego, Imperial, Riverside, Ventura, Kern, Tulare, Fresno and Madera Counties. “We have now been able to get significant numbers of traps placed in the Central Valley, where to date no psyllid finds have occurred,” said

makes its way into the Central Valley so growers can treat.”

According to Rick Dunn, CRB Data, Information, and Management Director, the techniques for detecting ACP range from using sticky panel traps placed in host trees to vacuuming host plant foliage. CRB currently has nine field technicians servicing approximately 3,500 traps spanning over 140,000 acres of commercial citrus, and the plan is to increase personnel and trapping as sum-mer approaches. “In working with the Board, we determined the best course of action was to start in the southern part of

Taylor, “and we are working towards an early detection system that gives us the best odds of identifying when the psyllid

Lab technician Kevin Kwok confirming ACP under high magnification.

Dr. Cynthia LeVesque, director of the CRB diagnostic laboratory in Riverside.


M.L. Roose and T.E. WilliamsDepartment of Botany and Plant Sciences, University of California Riverside

Since 1995 the citrus scion breed-ing program at the University of California Riverside has been

pursuing a mutation breeding program to develop new low-seeded selections through irradiation of buds from exist-ing high quality citrus cultivars, many of which were mandarins developed by the University of California or by USDA in California. ‘DaisySL’, a low-seeded, mid-season maturing mandarin selection is one of the more recent re-sults of that breeding program. In 1997 buds of ‘Daisy’ mandarin, a very high quality mid-season maturing mandarin originally developed by the U.S.D.A. Citrus and Date Station in Indio, were exposed to radiation (rather like an X-ray) to induce mutations. Trees were propagated from these irradi-ated buds and one of these trees was selected as having low seed content. A pathogen-tested bud source was established and ad-ditional trees were propagated and evaluated in replicated tri-als over many years in various parts of California. This selec-tion was released in August 2009 and named ‘DaisySL’. ‘DaisySL’

‘DaisySL’ Mandarinmandarin that combines medium-large sized fruit of excellent quality and pro-duction with a very low seed content, even in mixed plantings. It will likely be successful in a mid-season market-ing window, between Clementines and W. Murcott/’Tango’, that currently has very few low-seeded cultivars. Cur-rently, most fruit available at this mid-season time are stored Clementines or early harvest W. Murcott, and ‘Dai-sySL’ fruit should be of better quality than either of these alternatives.

Fruit Characteristics: Fruit of ‘DaisySL’ are generally round-ed in shape with a slightly

tapered stem end but with no neck. The fruit is large-sized for a mandarin (clas-sified as Jumbo by State of California

standards and Size 21 for Califor-nia industry packing standards) averaging 2.67 in (68.0 mm) in diameter and 2.37 in (60.1 mm) in height with a very smooth, deep orange rind color and slightly conspicuous, slightly raised oil glands. The rind is moderately adherent at maturity and rela-tively thin, averaging 0.12 in (3.0 mm) in thickness. Fruit are only moderately easy to peel. The thin rind is implicated in the tendency of ‘DaisySL’ and its parent variety ‘Daisy’ to occasionally experience a moderately high level of split-ting of fruit, sometimes as high Fruit of ‘DaisySL’ from Riverside.

is very low seeded (2.2 seeds/fruit) in all situations of cross-pollination, dif-fering from ‘Daisy’ which will set from 16-25 seeds/fruit in cross-pollinated sit-uations. The low seed content of ‘Dai-sySL’ under cross pollination should allow smaller growers to produce fruit with low seed content even though they cannot control the varieties grown by their neighbors and bees are present in the area. Fruit of ‘DaisySL’ are likely to have even lower low seed counts if other varieties that produce viable pol-len are not grown nearby, but this has not been measured as yet. ‘DaisySL’ was known throughout experimental evaluation as Daisy IR1 (for DAISY IRradiated selection #1). In summary, ‘DaisySL’ is a mid-season maturing

the state where ACP populations were being identified in urban areas and work our way north, ultimately getting ahead of the pest,” said Taylor.

To handle the inspection of traps and testing of psyllids and plant material, CRB opened a diagnostic lab in August of 2009 in Riverside. According to Dr. Cynthia LeVesque, Lab Director, “the lab is currently testing plant samples for HLB and conducting trap inspections for ACP, and when an ACP find occurs the lab then tests the psyllid for HLB. Our protocol for running both ACP and plant material samples is based on the best science and technology available, and we are confident in the accuracy and efficiency of our testing. The lab staff

continues to inspect traps and run tests on psyllids and plant samples for HLB at an ever-increasing rate.”

In addition to inspecting the CRB commercial traps, the CRB Riverside lab has begun assisting CDFA in the inspection of traps from CDFA’s urban trapping program. Currently CDFA has traps in urban areas, primarily in south-ern California, and has identified large populations of ACP in the Los Angeles area where treatments have been ap-plied. The Board’s scope of programming is intended to augment and assist federal, state, and county efforts to detect, con-tain, and eradicate the ACP from urban areas in southern California before they can move into Commercial groves.

“CRB, through our operations, now provides the California citrus industry the most efficient, integrated, high ca-pacity ACP/HLB detection program in the world,” said CRB President Batkin, “and we’re not stopping here.” CRB’s resolve against this monumental threat was evident at their annual meeting in October 2009, when the Board ap-proved research funding totaling $2.7 million; nearly $2.2 million of which has an application in the fight against ACP/HLB. “From projects that study the ef-ficacy of materials in treating psyllids to HLB resistance varietal development, CRB is committed to developing long-term solutions,” said Batkin. “We will prevail!” l


upright growth habit. Nine-year-old ‘Daisy’ trees were nearly identical in size. ‘DaisySL’ is not thorny. ‘DaisySL’ pollen has about 10-20% germination and fruit from hand pollinations onto Clementine or W. Murcott had only 1-2 seeds per fruit. This indicates that ‘Dai-sySL’ can be planted near these other cultivars without much risk of inducing high seed content in them.

Full fruit production of ‘DaisySL’ begins in the third year after planting similar to ‘Daisy’. A few fruit will set in the second year after planting but not at commercially acceptable levels. Fruit production on four-year-old trees averaged 59-160 lb (27-48 kg) at four fruiting trial sites. The original tree at Riverside was similar in fruit produc-tion in the fourth year and in years 7, 8 and 9 yielded 169, 70 and 158 lb of fruit

Eight-year-old ‘DaisySL’ mother tree on Carrizo citrange rootstock.

Fruit cluster from young ‘DaisySL tree on Carrizo citrange at Santa Paula.

respectively indicating that in the early years of production the variety has a tendency to alternate bear, similar to ‘Daisy’. It is likely that alter-nate bearing can be reduced by hand pruning to remove vigorous branches and main-tain a rounded crown, but this has not yet been tested.

Cultural practices: ‘DaisySL’ manda-rin can be grown

according to accepted cul-tural practices for most man-darin varieties including planting densities of 150-250 trees per acre (375-625 trees/ha), normal fertilization and pest control practices, and the use of standard rootstocks for mandarins including Carrizo, C35, and

trifoliate orange. Pruning may enhance production and health of the tree if ap-plied after the second year of full fruit production. Other rootstocks adapted to more marginal growing conditions of salinity, high pH or very heavy soils may be useful in those conditions, but have not been tested for compatibility.

Release and Distribution: ‘DaisySL’ was released for propagation in California in

September 2009. ‘DaisySL’ has been submitted for patenting by the Regents, University of California. A license to propagate the variety is available to any CDFA licensed California citrus nursery that purchases said license. Budwood for ‘DaisySL’ is being dis-tributed to licensed nurseries from registered screen-protected trees by the University of California Citrus

Clonal Protection Program. We expect that the initial bud supply will be used mainly to produce increase trees, so grower trees will probably not be available in significant numbers until spring or sum-mer of 2011. Growers should check with nurseries concern-ing tree availability. A three year exclusive propagation period for California nurser-ies will be enforced. Licenses for propagation outside the U.S. are being negotiated, but will not take effect until at least September 2012. l

a 20% of the total crop. The fruit interior has very deep orange flesh with a fine flesh texture, 10-11 segments and a semi-solid axis of medium size at maturity. The fruit are very juicy averaging 47% juice and about 5oz. (135 g) /fruit in weight. Flavor is rich, sweet and very distinctive when mature. Fruit from trees on Carrizo and C35 citrange rootstock average 11.9-12.8% soluble solids and 0.89-1.28% acid in mid-December at six trial sites in California, in-creasing to 14.2-15.8% soluble solids and 0.77-0.92% acid in early February at the same trial sites. In Riverside, Cali-fornia ‘DaisySL’ matures in winter (mid-December) and holds its fruit quality charac-teristics into February. Maturity in the San Joaquin Valley is similar or slightly later, whereas in the Coachella Valley it is earlier. The fruit average 2.2 seeds/fruit in the presence of substantial cross-pollination pressure across all trials sites. The fruit does not store well on the tree. Growth regulator sprays have not been evaluated. Limited postharvest storage tests suggest that it will not store well beyond about 30 days.

Tree Characteristics: Tree size, growth and fruit production characteristics and rootstock

comparisons have been evaluated in tri-als of ‘DaisySL’ in comparison to ‘Daisy’ mandarin from the same field blocks. Six-year-old ‘DaisySL’ trees in trials at Riverside, and four-year-old trees at the other six sites have been evaluated for two to four years of fruiting. Tree size and growth characteristics of ‘DaisySL’ have been consis-tent with ‘Daisy’ throughout the evalutions. Growth of both ‘Daisy’ and the ‘DaisySL’ selection have been quite spreading (characterized as ‘leggy’) in the first several years of growth followed by a tendency to grow into a more spherical, slightly droop-ing shape in ensuing years. The nine-year-old “DaisySL’ mother tree at Riverside on Carrizo citrange rootstock is 10.8 ft (3.3 m) high and 12.1 ft (3.7 m) wide with a normal


The California Citrus Research Board and Vision Robotics have been collaborating on vision-

based robotic harvester for fresh citrus. The project was renewed in October, and both are enthusiastic about testing that was completed this fall.

To date, mechanized attempts at har-vesting fruit for the fresh market have achieved limited success, and none of the prior solutions are economically viable. There are several distinct reasons for the lack of success including damage to the fruit, slow harvest speeds, and poor thor-oughness. Regardless of the specifics, the definition of success is economics; a sys-tem must operate with high quality and pick enough fruit fast enough to be cost

Vision Robotics successfully tests scout robot

effective relative to hand harvesting. This is a difficult proposition because it is expensive to build a robotic harvest-ing machine with sensors to detect the oranges, dexterous arms and picking hands, bin handling and a fruit conveyor. In order to compensate for the expense of the machine, it must pick fast and with high quality (very thorough and minimal damage to the fruit). Current prototype harvesting robots have typically picked two-thirds of the oranges at a speed ap-proximately half of what is required for economic viability.

The Vision Robotics DifferenceThese requirements led Vision Ro-

botics to its breakthrough approach of

separating the harvesting into two dis-tinct tasks, Scouting and Picking. While it may seem counterintuitive, adding the scouting system and its relative ex-pense is more than compensated by the improved harvesting speed and quality. As currently conceived, the Scout is a smaller independent robot that scans the trees prior to harvest to determine fruit position. This information is then used by the Picker robot to enable it to quickly and thoroughly harvest the tree.

Once the Scout was conceived it was easy to see other uses such as estimating crop load. Either scouting all of the trees or a statistical sampling will yield a crop load estimate accurate to within 95% including sizing. Knowing this informa-

Vision Robotics prototype orange Scout scanning trees.


tion prior to harvesting will enable better matching of the harvest to the orders. Even with manual harvesting, the grower can select the block with the oranges best sized to match the order and limit the harvest to the number of trees needed to fill the order. The remainder of the block can remain unpicked and the fruit continue to grow and get sweeter until it is needed to fill a later order. In addition, the Scout can include other sensors to detect disease, insect infestation or other stresses on the trees.

The Scout and How it WorksAt this time, the CRB and Vision

Robotics are moving forward with developing the Scout robot. Scouting involves mapping the trees to detect oranges, determine their location and sizes, and determine the possible ap-proach vectors for the picking hand. It does this by taking pictures along a grid on the outside of the tree. With a dense enough grid, located close to the canopy, the Scout can see virtually all the oranges even on large lush trees.

To estimate a crop load, the Scout software analyzes the images captured by the cameras, searching for fruit con-

tained within. This detection consists of two main software components, which are referred to as the back end and the front end of the detection algorithms. The front end considers images on an individual basis and classifies regions which could potentially be parts of or-anges. Combining information from left and right stereo image pairs, it passes a list of candidate oranges to the back-end portion of the software. The back-end portion tracks these candidate oranges between frames and across cameras, and ultimately decides which candidate oranges are actual oranges.

Field Test ResultsVision Robotics is working on the

Scout with both the citrus and apple industries. While the specific implemen-tations are different, the fruit detection and sizing system are virtually identical. The most recent field tests were con-ducted in apple orchards in October, but the results are applicable to both crops. To enable a concrete analysis, a team from the Washington Tree Fruit Research Commission hand collected crop data from 100’ sections rows. Each 100’ section was divided into segments,

and the number and size of apples con-tained within each was recorded.

In order to evaluate the front-end portion of the estimation software, 33 images were selected at random from scans of each of two different apple varieties. For each image, a human identified the number of human-visible fruit which were correctly detected by the software and the total number of human-visible apples. The front end admits many more regions than are truly apples (since the back end will determine which are true apples based on information across multiple frames) with very few missed fruit. For one set of images, all 169 apples were correctly flagged by the front-end software. The results for the second set of images were similar but slightly ambiguous because the apples were very clustered and it was difficult to determine whether all the apples in a cluster where individu-ally identified.

The next stage in analyzing the system performance was to determine the number of human-identifiable apples that were correctly identified by the back-end portion of the software as well as the number false positives

In this test with apple trees, the circles represent fruit identified by the Scout.


produced by the system, as identified by a human. Of the 169 apples in the 33 randomly selected images, 155 were correctly detected, 14 missed, and 27 falsely detected. This is a 92% percent accuracy rate for our first attempt, and Vision Robotics has identified the path to improving the performance. For example, falsely detected fruit are primarily caused by misalignment between camera pairs and the fact that the background dirt is red in color; both issues are easily resolved.

Comparing the Scout’s crop load estimates with the hand-counted values was the final analysis. For one of the hand-counted sections, the Scout’s count was 576, apples and the actual count was 565 for one apple variety. The average relative crop load estimation error ((es-timated yield – true yield) / true yield) was 2%. These estimates were observed to be above and below the true counts per 3’ region, suggesting a close match to the true yield distribution. For a smaller section of the second variety, the Scout counted 138 versus 162 for the hand count, or an average relatively error of -14.81%. These estimates are lower than the true counts, in part due to the soft-ware missing individual fruit in the cen-ters of large clusters. These observations help guide the planned improvements to the estimation software. It is believed that, in addition to enhancements to both the front and back ends of the software, the incorporation of a statisti-cal model will improve load estimates, particularly for fruit growing in clumps.

Orange Testing Begins in the SpringVision Robotics is currently integrat-

ing the citrus version of the detection software on the orange Scout. Field tests in orange groves are expected during the spring. Vision Robotics anticipates the detection algorithms will work at least as well on oranges due to the color contrast between the oranges and the rest of the grove. Moreover, the cameras on the orange Scout are mounted on the end of an arm that follows the tree canopy as opposed to a single vertical mast on the apple Scout. Mounting the cameras on the arm gives excellent views of the fruit, but large trees require fruit detection deep in the canopies and the scanning system collects significantly more images for processing. The first set of results will be available early in the summer. l

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500 N. Santa Fe, VisaliaLicense # 0A96361 • # 0011334

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Larry Lindgren, Grower; Ben Faber, UC Farm Advisor, Ventura Co.

Topworking or replanting, A grower’s perspective?

Second year stump grafted ‘Powell’ navel tree (left) versus a 6-year replant (right).

There are many changes going on in the citrus industry and one such opportunity is the conversion of

an orchard to another variety of citrus. If this is a consideration, then the question becomes one of whether the orchard should be topworked or replanted with new nursery trees. If the trees are healthy and under 20 years of age (it is pos-sible but not common to topwork older trees) and the new scion is compatible with the interstock or rootstock, then a topworked tree can bring the trees into production sooner than a replant. If the planting density needs to be changed, or serious soil preparation is needed, or a new irrigation system needs to be installed, then replanting would be the preferred choice.

The conversion choice is also de-pendent on the availability of new trees and budwood. New varieties are often in short supply. For either option, it’s best to make sure that the plant material is there. For topworking, T-budding conserves plant material more than stick grafting. If topworking is chosen, then it must be decided whether to graft the scaffold branches or the stump. Stump grafting makes for a shorter tree, but scaffold grafting reduces the risk of losing the topworked tree from graft damage due to birds, pests, wind or frost.

Several steps are required for top-working that will ensure success. These are listed below:• Get a reputable person to do the work.• Time of year is critical for grafting.

Spring is best for successful grafting.• Leave a nurse limb.• Decide to stump or scaffold graft.

- Stump grafting requires only 3 – 4 buds or sticks

- Scaffold grafting requires 2 buds per scaffold. Consider winds since even one year old unions are very tender.

• Sequence of events - Line up budwood - Remove top of tree and stack brush - Whitewash trunks - Paint cutoff surfaces - Insert grafts - Wrap grafts with plastic tape - Place white paper bag over grafts

and tape in place Later - Keep after ants and snails - Shred brush - Remove bags when shoots start grow-

ing through them. - Bi-monthly, in first year, brush out

water sprouts. Less often in the next 2 years.Much of this work can be contracted

with the grafter, who assures some level of performance, such as 90% take of the buds. It is up to the grower to ensure that pests do not damage the grafts.

It is often assumed that topworking is cheaper than replanting, but as the fol-lowing example shows, that is not true ini-tially. In Santa Paula, an ‘Olinda’ Valencia orchard on Carrizo citrange rootstock was interplanted in 1998 and 2000 with ‘Allen Eureka’ lemon on Macrophylla rootstock or ‘Powell’ or ‘Chislett’ navels on Carizzo or C-35 rootstocks. In 2002 and 2003 the ‘Olinda’ were topworked with ‘Allen Eureka’ lemons or ‘Powell’ navels. In a few cases, the ‘Allen Eureka’ lemons were stump grafted, but most trees were scaffold grafted. Table 1 shows

the costs for topworking and replanting this orchard. The costs of topworking are associated with the costs of the budwood (as much as $3 per tree), the act of graft-ing (depending on stump or scaffold, $8-10 per tree) and water sprout removal. Sprout removal is recommended six times in year one, eight times in year two and only four times in year three. At a labor rate of $12 per hour, sprout removal costs $7.20 per tree. The costs of replanting are $10-13 for the tree and $2.50 for planting the tree.

In the case of both the lemons and navels it cost more to topwork, but the topworking provides earlier production by 2 years and so gains the economic advantage. For example, if cultural costs are $1000 per acre per year (20 by 20 ft. spacing) and, conservatively, two years are saved, the maintenance savings would be $18 per tree over the 2 years. In the above study, the time advantage was even greater. The photo shows that three-year-old topworked lemons were similar in size and produced about the same as 6-year old lemon replants. Two-year-old topworked ‘Powell’ navels had a sig-nificantly larger canopy than six-year old replant navels and appear to have about the same fruit set for the coming year. Our conclusion is that the decision to topwork or replant depends on your situ-ation. Topworked trees produce sooner, but the conversion costs are higher and you have to have young healthy trees that you can successfully graft. l

Replant Topwork Lemons Tree $10.50 Graft $8.00 Planting 2.50 Sproutremoval 7.20 Total $13.00 $15.20LateNavels Tree $12.50 Royaltyforbuds $2.25 Planting 2.50 Graft 8.00 Sproutremoval 7.20 Total $15.00 $17.45

Comparison of costs of replant and topworking of an ‘Olinda’ Valencia orchard to lemons and navels.


Third year scaffold grafted ‘Allen Eureka’ lemon (right) compared to a 6-year replant (left).

Second year ‘Powell’navel scaffold branch suckers need to be removed so they don’t overwhelm the graft.


Citrus quick decline:a disease complex

In August 2009, the UCCE farm advi-sor for Tulare County reported citrus quick decline (QD) of sweet orange

trees in old orchards (at least 50 years) that presumably were grafted on sour orange (SO) rootstock (Fig. 1). These orchards were primarily in the Lindsay and Exeter area within the San Joaquin Valley of California. It is estimated that 150-200 acres of orchards were afflicted with declining trees. After showing general decline symptoms, affected

trees collapsed within a few weeks and died. Bud union symptoms included “honeycombing” or “inverse stem pit-ting,” which appears as numerous tiny pegs on the side of the wood and cor-responding pinholes on the side of the bark. Just below the bud-union a yellow to light brown discolored zone was also observed. This combination of symptoms is seen on sweet orange, grapefruit, and tangerines on SO and is typical of quick decline of citrus, caused by the Citrus tristeza virus (CTV) (Fig.2). Additionally, roots showed stained grayish brown to purple lesions in the bark of large scaf-

fold roots, which is characteristic of dry root rot symptoms caused by Fusarium solani (Fig.3A).

Tristeza-CTV: During the nineteenth century, a root rot epidemic caused by Phytophthora spp. destroyed seedlings of sweet orange trees and forced the adaptation of Phytophthora-tolerant SO rootstock (6). Phytophthora species are Oomycetes, closely related to water molds that behave like fungi. In the beginning of the twentieth century, cit-riculture expanded worldwide and large quantities of citrus plants were shipped from areas where CTV originated to

Akif Eskalen, Georgios Vidalakis, Neil O’Connell

Fig1. Quick decline of sweet orange (Valencia) trees in the Central Valley during the summer of 2009.

Fig 2. Bud union symptoms of CTV infected sweet orange on sour orange rootstock. Bud union of declining tree with honeycombing on the wood and small pinholes on the bark (left). B) Bud union of healthy tree (right).

Fig 3. Root symptoms of quick declining trees on sour orange rootstock. A) Dark decay in the bark of large scaffold roots B) Cross section of dark decay in a root. C) Potassium iodide test of declining tree lacking starch (no color) D) and healthy tree with starch (dark blue color).


References1. Bar-Joseph, M., Marcus,R., Lee, F.R.

1989. The Continuous challenge of citrus tristeza virus control. An. Rev. Phytopathol. 27:291-316.

2. Bender, G.S., J.A. Menge, H.D. Ohr and R.M. Burns. 1982. Dry root rot of citrus: its meaning for the grower. Citrograph 67(11):249-254.

3. Brown, L.G., Denmark, H.A., Yokomi, R.K. 1988. Citrus Tristeza Virus and its vectors in Florida. Plant Pathology Circular. No:311.

4. Fawcett, H. S . , Wallace, J . M . 1946. Evidence of the virus nature of citrus quick decline. Calif. Citrogr. 32:88-89.

5. Garnsey, S. M., M. Bar-Joseph, F. Lee. 1981. Applications of serological indexing to develop control strategies for citrus tristeza virus. Proc. Int. Soc. Citriculture 1:448-452.

6. Garnsey, S.M., Young, R.H. 1975. Water flow rates and starch reserves in roots from citrus trees affected by blight and tristeza. Agricultural Research Service, USDA Orlando.

7. Klotz, L. J. 1978. Fungal, bacterial, and nonparasitic diseases and injuries originating in the seedbed nursery and orchard. In The Citrus Industry, ed. W. Reuther, E.C . Calavan, G.E. Carman, Vol. 4. Berkeley, Calif: Div. Agric. Sci. Univ. Calif.

8. Wallace, J. M. 1 978. Virus and virus-like diseases. See Ref. 93, pp. 67-18.

CTV-free areas, spreading the disease around the world (1,7). During this time, the first serious decline epidemic of sweet orange trees on SO rootstock was recorded in most citrus growing areas of the world. More than 60 million trees died worldwide, and the disease was named “tristeza” from the Spanish and Portuguese word for “sadness”. Califor-nia was hit by this tristeza epidemic in 1939 and since then CTV has become established throughout the state (1, 3).

CTV is a phloem-limited virus that is transmitted by aphids. It can also be spread through grafting infected plant material. In addition to the above symp-toms, previous studies showed that CTV causes a girdling effect at the bud union of trees on SO, thereby depleting starch to the root system and debilitating feeder roots (4, 5).

Dry root rot- Fusarium solani: Dry root rot is a destructive disease of citrus, caused by the fungus Fusarium solani. The fungus begins as a weak pathogen, colonizing the outer portion of larger roots and spreads up into the crown (Fig. 3A). The wood below the dead bark is hard, dry, and stained grayish brown to purple and the lesion extends deep into the wood (Fig. 3B). When the plant is under stress, and/or root starch is depleted, the fungus colonizes rapidly and causes extensive root damage, with leaves suddenly wilting and dying on the tree. (2). Dry root rot has been reported from citrus growing areas worldwide including California. F. solani is also often involved in Phytophthora root rot caused by Phytophthora nicotianae.

Hypothesis and Study: Based on the observed symptoms and the biology of the fungus, we hypothesized that inter-actions between CTV, F. solani, and/or Phytophthora nicotiana potentially play a role in the QD problem observed in Tulare County.

Three orchards with quick declining citrus were studied in Tulare County in August of 2009. Leaf, shoot, bark, and root samples from advanced declining, declining, and healthy looking trees were collected. Leaf, shoot, and bark material were tested for CTV using ELISA (En-zyme-Linked Immunosorbent Assay), and RT-PCR (Reserve Transcription Polymerase Chain Reaction). Rootstock bark was genetically analyzed at Dr. M. Roose’s UCR laboratory to verify that they were SO rootstocks. Roots were plated onto different culture media in

order to isolate fungal and bacterial pathogens. Fungal and bacterial cultures were further processed for molecular identification. To assess tree girdling at the bud union by CTV, presence of starch in roots was determined by dip-ping roots in 2% potassium iodide and 0.2% elemental iodine solution (5). Starch absence (no color) indicates a tree with starch depleted roots caused by a girdling effect (Fig 3C). Roots with starch (dark blue color) are indicated as not stressed or girdled at the bud union (Fig. 3D).

Laboratory tests showed that the advanced decline and declining trees were consistently infected with CTV and F. solani. F. solani and CTV were never recovered from the healthy looking trees (Table 1). The roots of declining trees were also starch depleted (Table 1, Fig 3. C), which indicates that the plant were under stress because of the girdling at the bud union caused by infection of CTV.

Previous studies have shown that F. solani infections occur when trees are stressed by lack of water, poor nutrition, freeze damage and most often when trees are girdled (2). In this investiga-tion, the presence of F. solani on starch depleted CTV girdled trees corroborates results from previous studies. Because F. solani was recovered only from trees on which CTV was present, it is likely that the QD observed in Tulare County is not the result of a single pathogen, but the result of a disease complex in which trees are predisposed to root stress by CTV and are rapidly dying by an additional infestation of F. solani. Control for this disease complex is currently unknown; however removal of trees infected with

Akif Eskalen and Georgios Vidalakis are University of California, Coopera-tive Extension Specialists and Plant Pa-thologists, Department of Plant Pathology and Microbiology, UC Riverside; Neil O’Connell is Farm Advisor, University of California Cooperative Extension Tulare County. l

Tree Rootstock CTV Iodine F. solani Phytophthora sp. Condition Starchtest

advanced decline Sour orange + - + +

orchard 1 declining Sour orange + - + -

healthy looking Sour orange - ++* - -

advanced decline Sour orange + - + -


healthy looking Sour orange - + - -

advanced decline Sour orange + - + -


healthy looking Cleopatra - ++* - - mandarin*++Indicates high levels of starch

Table1.Pathogendetection,starchanalysis,androotstockgeneticprofileofsweetorangefromTulareCountyinCalifornia

CTV to prevent QD spread to healthy trees in California should be considered. The Eskalen laboratory is currently investigating to determine control mea-sures for dry root rot.

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“Everywhere we see the seeds of the same growth that America itself has known.” - Dwight D. Eisenhower

While speaking to a global audience, the words of President Eisenhower’s Second Inaugural Address could be just as easily applied to the world of Andrew Duda. In 1909, he came to America where he started with a dream, a deeply rooted work ethic and a small, 40-acre family farm in Central Florida. Today, as a global provider of fresh citrus, celery and other produce, Duda Farm Fresh Foods is part of DUDA, which is still family-owned, quality–and customer-focused, yet more diversifi ed and bigger than we ever dreamed. If you’d like to take part in our dream, contact Duda Farm Fresh Foods at 866-792-DUDA or dudafresh.com.

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